Injury may result if this procedure is not followed properly. Use caution and follow all warnings.

Introduction

Follow the steps in this guide to remove or replace the heat sink in a 21.5" Retina 4K 2017 iMac.

Some images in this guide use a 2015 iMac, which has minor visual differences. These differences do not affect the repair procedure.

This guide is marked "potentially dangerous" because it requires you to handle a power supply that contains large capacitors. Unplug the iMac and hold the power button down for at least 10 seconds to help discharge the capacitors. Handle the board by the edges and do not touch surface components.

The wedge is an extremely tight fit for this model. I was worried that the amount of force needed to use it as shown might damage the stand, so I used it with the long side down instead. It worked fine that way and didn’t need anywhere near as much force to insert.

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Starting on the left of the display, near the power button, insert the iMac Opening Tool into the gap between the glass panel and the rear enclosure.

The hub on the iMac Opening Tool will keep you from pushing the wheel in too far. If using a different tool, insert no more than 3/8" into the display. Otherwise, you risk severing antenna cables and causing serious damage.

Hi! Actually - there is no need to cut the tape around the camera area - there is no tape to cut at all! And so, the way go is easy - just pass 10 mm to the left and to the right from camera and start cutting!

P.S. Just did the whole procedure to replace a RAM and to add SSD on PSIe an hour ago! Seems to be different reading the instructions... you know - 2/10 and so on. But it's really not that hard, trust me. I'll give it 5/10.

P.P.S. By the way there is one trick to pass the difficult steps. Any action which requires pulling smth (motherboard, speaker, power supply unit) from the narrow crack (or should i say - slit?) at the bottom of your Imac is really not so easy.

And the trick is to first remove a thin metal stripe with some kind of insulation on it which held by 5 small (very small!!) screws at the bottom of your Imac. After you done it - it's easy to pull everything! Pay attention to the fact that one of this 5 screws at the center are more shortly than others.

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At this point there is still a strip of adhesive along the bottom of the display that will hold the display to the frame like a hinge. You can loosen this adhesive by working the display up and down a few times.

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At step 21-22, releasing the adhesive strips from the bottom of the display, I noticed a tab on the outer end of each strip. Pull the tab to remove the whole strip, no need to mess around with the plastic cards!

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The next few steps bring your hands close to the exposed face of the power supply. Do not touch the face of the power supply or any of the exposed solder. Touching it risks a high voltage shock from the many large capacitors attached to the board.

Use the tip of a spudger to push each side of the power button cable connector and gently walk it out of its socket.

And DON’T do what I did, which is to remove the left speaker - which can easily lead to breaking the cable between the power on button and the power supply. The cable is routed through a hidden slot at the very bottom of the left speaker

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Peel off the four black tamper-evident stickers covering the heat sink mounting screws.

Remove the four T10 screws that secure the heat sink from the backside of the logic board.

During reassembly, tighten these screws one full turn at a time, alternating in a cross pattern. This will gradually increase the clamping pressure evenly across the surface of the CPU. Continue gradually tightening the screws until they're snug and the entire spring plate lays flat against the logic board.

Resources

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